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Re: [Xen-devel] [PATCH] libxl: change default QEMU machine to pc-i440fx-1.6

Il 25/05/2014 16:14, Stefano Stabellini ha scritto:
On Fri, 23 May 2014, Fabio Fantoni wrote:
Il 23/05/2014 18:07, Stefano Stabellini ha scritto:
Choose pc-i440fx-1.6 instead of pc for HVM guests, so that we know for
sure what is the machine that we are emulating.

Use pc-i440fx-1.6 regardless of the xen_platform_pci option. Add the
xen-platform device if requested. Choose slot 2 for the xen-platform
device for compatibility with current installations. In case of Intel
graphic passthrough, slot 2 might be needed by the grafic card. However
now that we can specify the slot explicitly, it is easy to change the
position of the xen-platform device on the PCI bus if graphic
passthrough is enabled.

Move the machine options earlier, before any other emulated devices
options. Otherwise the selected PCI slot for the xen-platform device is
not available in QEMU.

Specify PIIX4_PM.acpi-pci-hotplug-with-bridge-support=off, because
differently from xenfv, the other QEMU machines do not have that option
off by default.

This patch does not change the emulated environment in the guest.

Refer to this thread: http://marc.info/?l=xen-devel&m=140023775929625&w=2

Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>

diff --git a/tools/libxl/libxl_dm.c b/tools/libxl/libxl_dm.c
index 8abed7b..fef684f 100644
--- a/tools/libxl/libxl_dm.c
+++ b/tools/libxl/libxl_dm.c
@@ -476,6 +476,29 @@ static char **
libxl__build_device_model_args_new(libxl__gc *gc,
           flexarray_vappend(dm_args, "-k", keymap, NULL);
   +    flexarray_append(dm_args, "-machine");
+    switch (b_info->type) {
+        flexarray_append(dm_args, "xenpv");
+        for (i = 0; b_info->extra_pv && b_info->extra_pv[i] != NULL; i++)
+            flexarray_append(dm_args, b_info->extra_pv[i]);
+        break;
+        flexarray_append(dm_args, "pc-i440fx-1.6,accel=xen");

I think that a note in README should be added: qemu >=1.6.1 is required for hvm domUs.

About the other xl parameter to be added I think that should be:
qemu_machine_type="i440fx"|"q35" (when also q35 will be supported on xen)
qemu_machine_version="x.y" to specify the machine version, useful for debug/testing and other some cases.

+        flexarray_append(dm_args, "-global");
+        flexarray_append(dm_args,
I think is good add a comment for remember to remove this workaround when pc
=2.1 will be the default since qemu 2.1 will fix it.
The workaround is not actually harmful, it doesn't need to be removed
when pc >= 2.1 in QEMU.

+        if (libxl_defbool_val(b_info->u.hvm.xen_platform_pci)) {
+            flexarray_append(dm_args, "-device");
+            flexarray_append(dm_args, "xen-platform,addr=0x2");
The fixed pci address to 0x2 probably is a problem with intel gpu passthrough:
Right, however we cannot really change the default position of the
xen-platform device on the PCI bus, otherwise we'll end up changing the
emulated environment for all the VMs out there.

I'll leave it to Tiejun to move xen-platform to another slot when
graphic passthrough is enabled.

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